Artificial Intelligence

1. 1
Contents
LISP and Other AI programming Language
Introduction to LISP
LISP: Syntax and Numeric Functions
List Manipulation function in LISP

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Introduction to LISP
LISP (LISt processing) is invented by Jhon McCarthy
during the late 1950.
The basic building blocks of LISP are the atom, list,
and the string.
 An atom is a number of string of contiguous
characters, including numbers and special characters
A List is a sequence of atoms and/or other lists
enclosed within parentheses.
String is a group of characters enclosed in double
quotation marks.

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Example of Atom, List & String
Atom: sat, week_day
List: (mon, tue, wed, thur, fri, sat, sun)
String: “please enter your name”
Atom, List and String are the only valid objects in LISP
and they are called Symbolic expression.
Any s-expression is potentially a valid program.

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Introduction: LISP
LISP programs run either on an interpreter or as
compiled code.
The interpreter examines source programs in a
repeated loop, called read-evaluate-print loop.
For example: sum of 3 numbers
-> (+ 5 6 9)
20
->
LISP uses prefix notation.

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Example of LISP
Convert Fahrenheit to Centigrade
C/5=(F-32)/9
or, F=C(9/5)+32
For C=50,
LISP program
->(+(*(/ 9 5)50)32)
122
->
Numerical functions: +, -, *, /

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Basic List Manipulation Functions
Function call Value
returned
Remarks
(car `(a b c)) a Car takes one argument, a list, and returns
the first element.
(cdr `(a b c)) (b c) Cdr takes one argument, a list, and returns
a list with the first element removed.
(cons `a`(b c)) (a b c) Cons takes two arguments, an element and
a list and returns a list with the element
inserted at the beginning.
(list `a`(b c)) (a (b c)) List takes any number arguments and
returns a list with the arguments as
elements.

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Basic List Manipulation Functions
Function call Value
returned
Remarks
(append `(a) `(b c)) (a b c) Merge two or more lists into a single list
(last `(a b c d)) (d) return a list containing the last element.
(member `b `( a b d)) (b d) Returns remainder of second argument list
starting with element matching first
argument.
(reverse `(a (b c) d)) (d (b c) a) returns a list with top elements in reverse
order.

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Example of (setq()) function
->(setq x `(a b c))
->x
A B C
->`x
X
->(setq x (+ 3 5))
8

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How to Define Function?
(defun name (parm1 parm2 …) body)
Example:
->(defun avgthree (n1 n2 n3) (/(+n1 n2 n3) 3))
AVGTHREE
->
Note: its return the function name. If you call this
function it will return the result.

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The Most Common Predicate calls
Function call Value
returned
Remarks
(atom `aabb) t aabb is a valid atom
(equal `a (car `(a b)) t
(evenp 3) nil
(oddp 3) t
(numberp 10ab) nil
(greaterp 2 4 27) t Arguments are successively larger
(lessp 5 3 12) nil Arguments are not successively
smaller
(listp `(a)) t Valid list
(zerop .0001) nil
(null nil) t Nil is an empty set

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Conditional Statement
 The syntax for condition is,
cond (<test1> <action1>)
(<test2> <action2>)
. .
. .
. .
(<testk>
<actionk>))
Example:
->(defun maxthree(a b c)
(cond ((>a b) (cond ((>a c) a)
(t c)))
((> b c) b)
(t c)))
MAXTHREE
->
->(maxthree 20 30 10)
30
->

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Input, Output Variables
read: ->(+ 5 (read))
6
11
->
print: ->(print`(a b c))
(A B C)
(A B C)
->(print
“hello”)
“hello”
“hello”
prinl: print without new line
princ: remove double quotation marks
terpri: it does not take arguments
It introduces a new line whenever it
appears and then returns nil.
->(defun circle-area()
(terpri)
(princ “Please enter the radius:”)
(setq radius (read))
(princ “ The area of the circle is:”)
(princ (* 3.1416 radius radius))
(terpri))
CIRCLE-AREA

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Input, Output Variables
->(defun circle-area()
(terpri)
(princ “Please enter the radius:”)
(setq radius (read))
(princ “ The area of the circle is:”)
(princ (* 3.1416 radius radius))
(terpri))
CIRCLE-AREA
->(circle-area)
Please enter the radius:
4
The area of the circle is:
50.2656
->

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Iteration
-> (defun factorial(n)
(do (count n (-count 1))
(product n (* product (-count 1))
((equal 0 count) product)))
FACTORIAL
->

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Property Lists and Arrays
One of the unique and most useful features
of LISP as an AI language is the ability to
assign properties to atoms.
Example: properties of a car are make, year,
color, style, etc.

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Property Lists and Arrays
 The function putprop assign properties to an atom or
objects
(purtop object value attribute)
->(putprop `car `toyota `make)
TOYOTA
->(putprop `car 1998 `year)
1998
->(putprop `car `red `color)
RED
->(putprop `car `four-door `style)
FOUR-DOOR

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Property Lists and Arrays
 remprop: remove properties
 get: retrieve property
Example:
-> (get `car `color)
RED
-> (remprop `car `color)
RED
->(get `car `color)
Nil
->

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Property Lists and Arrays
Arrays:
->(setf myarray (make-array `(10)))
#A(NIL NIL NIL NIL NIL NIL NIL NIL NIL NIL)
->
To access array:
->(aref myarray 9)
NIL
->
Store:
->(setf (aref myarray 0) 25)
25
->

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PROLOG
PROLOG (PROgramming in LOGic)
Invented by Alain Colmerauer, 1970.
Programming in PROLOG is accomplished by
creating a data base of facts and rules about objects,
their properties, and their relationships to other
objects.

20. PROLOG
 PROLOG means PROgramming in
LOGic
– The programmer uses the system to
draw inferences from facts and rules
 PROLOG is
– declarative - specify facts and logical
relationships
– symbolic - symbols are used to
represent objects
– high level - contains a built-in problem
solving mechanism
 PROLOG Programs
– solve problems by declaring objects
and their relationships

21. PROLOG Paradigm
PROLOG
database
Queries
Facts Rule
s
• The PROLOG Programmer
– Loads facts and rules into the database.
– Makes queries to the database to see if a
fact is:
• in the database or
• can be implied from the facts and rules
therein
Facts:
isa(dog, mammal).
isa = predicate
(dog, mammal) = argument
2 = binary

22. PROLOG Paradigm …
…
PROLOG
database
Queries
Facts Rule
s
 Predicates (clauses)
In this example, both “isa” and
“animal” are examples of predicates.
 Predicates are used to indicate
relations between objects and hence
can represent FACTS and RULES.
 Two ways to use predicates in a
query:
– 1. As a TRUE/FALSE test:
?- isa(dog, mammal).
yes
– 2. For DATA RETRIEVAL
?- isa(dog, X).
X = mammal

23. • Constants
– Atoms
• Alphanumeric atoms - alphabetic
character sequence starting with a lower
case letter
Examples: apple a1 apple_cart
• Quoted atoms - sequence of characters
surrounded by single quotes
Examples: ‘Apple’ ‘hello world’
• Symbolic atoms - sequence of symbolic
characters
Examples: & < > * - + >>
• Special atoms
Examples: ! ; [ ] {}
– Numbers
• Integers and Floating Point numbers
PROLOG syntax

24. PROLOG syntax … …
• Variable Names
A sequence of alphanumeric characters beginning with an
upper case letter or an underscore
Examples: Anything _var X
• Compound Terms (structures)
– an atom followed by an argument list containing terms. The
arguments are enclosed within brackets and separated by
commas
Example: isa(dog, mammal)

25. System Interaction
Reminder:
Problem solving in PROLOG
– 1. insert facts and rules into the database
– 2. ask questions (queries) based on the contents of the database
• Facts
– Used to represent unchanging information about objects and
their relationships.
– Only facts in the PROLOG database can be used for problem
solving.
– Insert facts into the database by,
• typing the facts into a file and loading (consulting) the file
into a running PROLOG system

26. • Queries
– Retrieve information from the database by entering
QUERIES
– A query,
• is a pattern that PROLOG is asked to match against
the database
• has the syntax of a compound query
• may contain variables
– A query will cause PROLOG to
• look at the database
• try to find a match for the query pattern
• execute the body of the matching head
• return an answer
System Interaction … …

27. System Interaction … …
Example:
Assume that the database contains:
– likes(hasan, rita).
– likes(belal, rita).
– likes(mohsin, beli).
The actual system interaction looks
like
?- likes(hasan, rita).
yes
?- likes(mohsin, rita).
no
?- likes(mohsin, X).
X = beli;

28. Variables in Prolog
Reminder: a variable starts with a
capital letter or underscore.
When a variable is used, PROLOG tries
to find a match (instantiation) for it.
?-likes(Who, rita).
Who = hasan;
Who = belal;
no

29. Simple
Backtracking
 PROLOG searches its database attempting to satisfy
a query (goal), stopping at the first success or
returning no for failure.
 Often, there will be more than one successful
match and the programmer would like to tell the
PROLOG system to try again and search for other
successful matches.
 When PROLOG retries a goal, it is called
backtracking.
 Backtracking may be forced by typing a ;

30. Examples: Backtracking
?- likes(Who, rita).
Who = hasan ;
Who = belal ;
no
?- likes(Who, Whoelse).
Who = hasan
Whoelse = rita ;
Who = belal
Whoelse = rita ;
Who = mohsin
Whoelse = beli ;
no
?- likes(Who, beli).
Who = mohsin
?- likes(hasan, Whom).
Whom = rita ;
no
?- likes(belal, Whom).
Whom = rita ;
no

31. Backtracking with Anonymous Variable
Suppose that you want to know if Hasan likes anyone and
do not care who in particular.
Then use the anonymous variable which is the character
“_”
It represents a different variable each time it occurs
?- likes(hasan, _).
yes
?- likes(_, _).
yes
Suppresses output of variable binding

32. Rules
 A PROLOG rule consists of one conclusion
followed by one or more conditions
– a fact is a rule with no conditions
– conclusion :-
condition1,
.....
condition N.
– read as:
 The conclusion is true if condition1 and condition2... and
condition N are true.
 Conditions are separated by commas
 Rules , facts and queries are all examples of Horn clauses -

33. Rules … …
 A PROLOG rule consists of a
head and a body
– head :-
body.
– read as:
 If a match is made on the
head, then carry out the body.

34. Arithmetic Functions/ Predicates
 Operators for the basic arithmetic operations
+, -, *, /, **, mod, // (integer division).
Examples:
?- 7+3=10. ? - X is 5/2
No ? - Y is 17//3.
?- 10 is 7+3. ?- Z is 23 mod 5.
Yes
 Predicates for the basic arithmetic operations
<, =<, >, >=, =.=, ==.
Examples:
?- 14-9=.=3+2. ? - 10 ==7+5.
Yes Yes

35. PROLOG syntax … …
 Lists
A sequence of terms of the form
[t1, t2, t3, t4, ..., tn]
where term ti is the ith element of the list
Examples:
[a,b,c] is a list of three elements a, b and c.
[[a,list,of,lists], and, numbers,[1,2,3]]
is a four element list.
[ ] is the ‘empty list’. It is an atom not a list data type

36. Knowledge from Semantic Net
Example:
The Queen Mary is an ocean liner.
Every ocean liner is a ship
ship
Ocean_liner
Queen_mary
IS-A
IS-A

37. Semantic Networks
 Knowledge is represented as a network or graph
animal
reptile
elephant
Nellie
mammal
apples
large
head
subclass subclass
HAS_PART
subclass
instance
LIKES
SIZE
africa
LIVES_IN